The invention relates to an arrangement for focusing reflecting telescopes, in particular, the small type astronomic reflecting telescopes in which a primary reflector is displaced along the optical axis for adjustment of the entire arrangement.
The journal "Der Sternenbote", Wien, 25th volume, 1982, 2 in particular at pages 24 and 26, discloses a reflecting telescope comprising a spheric primary reflector, a secondary reflector and Schmidt plate, in which the principle or primary reflector is displaceably seated on a socket attached to the rear housing portion for displacements along the optical axis.
The focusing of the telescope is performed by means of an adjustment screw which via a lever means displaces the principal reflector along the socket.
The lever is rigidly secured to the reflector mount. This device is disadvantageous since the point of force of the adjustment screw actuated lever means acts considerably eccentrically relative to the optical axis, and, hence, to the center of the reflector so that undesired tiltings of the reflector occur when the latter has to be focussed. Furthermore, a reversal of the direction of rotation of the adjustment screw involves a dead travel due to the unavoidable backlash between the cooperating members so that an accurate focusing is rendered difficult.